This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A major aim in structural biology is to design new proteins and control their function, including novel protein-to-protein signalling. The modular nature of proteins makes such engineering possible, but mechanisms by which component parts can be connected have not been fully elucidated. We have developed a simple method to couple the functions of two proteins, which we demonstrate here with light-triggered DNA binding. When illuminated, this fusion of a photoactive LOV domain and bacterial trp repressor selectively binds operator DNA upon illumination. This work suggests new ways of reprogramming cellular behaviors such as metabolism, morphology, and cell death. We are interested in investigating how large scale conformational changes are involved in the propagation of signals in our designed protein. Recent work has shown that some, and perhaps many, LOV domains respond to light with rather large structural changes. Our design strategy aims to take advantage of these changes, and measuring their magnitude and how they correlate with activity is an important means of validating our results. The SAXS experiments we have undertaken at BioCAT have been a critical part of this work. In some respects they have confirmed our expectations and in others they have challenged them and led us to refine our model. Paper accepted at PNAS pending minor revision: Light-activated DNA binding in a designed allosteric protein. Devin Strickland, Keith Moffat, and Tobin R. Sosnick